The present invention relates to liquid-permeable topsheets for use in disposable body fluid absorptive goods such as sanitary napkins, disposable diapers and training pants.
In liquid-permeable topsheets used for body fluid absorptive goods, a technique is well known to make the topsheet from plastic film or nonwoven fabric and provide some with liquid through passages extending from top to bottom thereof. An upper surface of the topsheet is adapted to contact the wearer's skin, and lower openings of the respective liquid passages contact an absorbent core so that capillary action occurring within each liquid passage may be utilized to transfer excreted body fluids toward the absorbent core.
For example, Japanese Patent Publication No. 1982-17081 discloses a technique according to which a topsheet made of polyethylene film is provided with conically tapered liquid passages and the lower ends of the respective passages are arranged so as to be closely in contact with an absorbent core.
According to a technique disclosed by Japanese patent application Disclosure Gazette No. 1985-259261, a topsheet made of plastic film is provided with cylindrical liquid passages with their lower ends extending into an absorbent core, on one side, and a fibrous layer is bonded to the lower surface of the topsheet with fibres thereof extending into the liquid passages, on the other side. Such cylindrical liquid passages are more stable and therefore less deformable than the conical liquid passages under the same large load. Additionally, the cylindrical liquid passages are preferred to the conical liquid passages in that the fibres extending into the liquid passages also contribute to accelerate body fluids to be transferred toward the absorbent core under the capillary action.
According to a technique disclosed by Japanese patent application Disclosure Gazette No. 1992-152945, there is provided a high density area or rib continuously surrounding lower openings of respective liquid passages. This technique certainly stabilizes the opening of each liquid passage against deformation as well as collapse and allows body fluids to be effectively transferred toward an absorbent core.
Soft touch is essential to a topsheet, and therefore such conventional topsheets as disclosed by the above-mentioned Patent Publication and Disclosure Gazettes are also made from thin and soft materials. However, a disadvantage of the conical liquid passages disclosed by said Japanese Patent Publication No. 1982-17081 as well as the cylindrical liquid passages as disclosed by Japanese patent application Disclosure Gazette No. 1985-259261, is that the lower openings, i.e., free ends of those liquid passages are liable to be deformed, so the liquid passages readily collapse, for example, under the body weight of a wearer and a body fluids are often prevented from being smoothly transferred toward the absorbent core. While stability of each liquid passage against a compressive force exerted axially on the liquid passage can be more or less improved, such a liquid passage is still ready collapsible under a force exerted transversely on it since it comprises soft material. While the technique disclosed by the above-mentioned Japanese patent application Disclosure Gazette No. 1992-152945 may theoretically alleviate the problem of collapse, both the thickness of the topsheet and diameter of the liquid passage are unfeasibly fine, so that it would not be easy to provide the previously mentioned high density area or rib continuously surrounding the lower openings of the respective liquid passages although this is one of the most important features of the disclosed technique.
In view of these problems, unsolved by the prior art, it is a principal object of the invention to provide a topsheet comprising a first sheet and a second sheet underlying said first sheet wherein said first sheet is provided with liquid passages and said second sheet is welded to said first sheet around the lower openings of the respective liquid passages so as to restrict possibly occurring deformation of the liquid passages and thereby to solve the problems encountered by the conventional topsheets.